The present invention relates to a method of solidifying liquid oils and a solidifying agent. More particularly, the present invention relates to the method of solidifying rapidly and easily waste oils such as used waste edible oils or waste engine oils of cars without heating and to the solidifying agent used therefore.
In recent years, water pollution of drains, rivers, lakes and the like has been a significant social problem from an environmental aspect and, among them, it is said that throwing away the used edible oils from general homes into drains is one of major causes for the pollution due to oils.
The used waste edible oils, if little, have been treated as inflammable trash after being absorbed into newspapers, cloths and the like. In case where an amount of the waste oils is large, however, since it is difficult to treat the waste oils by means of the absorption method, various kinds of methods of solidification-treatment of the waste oils with a gelling agent have been proposed in recent years. Though a certain method of those methods has already been commercialized (the following method (2)), it has not yet been spreaded sufficiently because problems such that it takes a long period of time to solidify the waste oils and that there is a danger of a fire caused by oil are not yet solved.
As the method of treatment by using the gelling agent, there are known a method (1) wherein a solidification-treating agent containing, as a main ingredient, a natural wax, a synthetic wax, a solid higher fatty acid, a solid higher alcohol or a resin having a melting point of not higher than 150.degree. C. is used for the solidification-treatment (JP-A-112385/1979), a method (2) wherein waste edible oils are solidified by adding 12-hydroxystearic acid to the waste edible oils, heating to dissolve the acid, and then cooling (JP-A-106298/1980), a method (3) wherein there is used a solidification-treating agent for disposal of waste edible oils containing a combination of 12-hydroxystearic acid and a small amount of a higher fatty acid having 16 to 24 carbon atoms or dibenzylidene sorbitol and a nuclear-substituted compound thereof as effective components (JP-A-19681/1986), a method (4) wherein waste edible oils are solidified by adding a solution of 12-hydroxystearic acid dissolved in a polar solvent such as dimethyl sulfoxide, N-methylpyrrolidone or ethyl alcohol to the waste edible oils and mixing them, and then bringing the obtained admixture into contact with water (JP-A-90599/1988), a method (5) wherein liquid oils are gelled by adding boric acid or a borate after the liquid oils are emulsified by adding a water-soluble macromolecular compound having hydroxyl group and water (JP-A-122796/1992), and the like.
Each of the above-mentioned methods (1) to (3) is, however, to solidify the waste oils by heating up to at least 80.degree. C. to dissolve the gelling agent therein and then cooling, and is neither economical nor efficient because a large energy and long time are required for heating and cooling the waste oils. Further, these methods have many problems such that there is a danger of getting scalded if the heated waste oils of high temperature are spilled, that there is a fear of a fire to be caused by heating the waste oils too high, and that bad smell due to deterioration of the waste oils are generated during the heating. Particularly, in case where the amount of oil is about four liters like waste engine oil from a car and is several times larger than that of the waste edible oil generated in the general home, a danger of scalding and fire is further increased. Therefore, it cannot be recommended in view of safety to carry out the solidification-treatment of the waste engine oils (hereinafter abbreviated simply to "waste-oil-treatment") at general homes according to methods (1) to (3). The method (4) is different from methods (1) to (3) and is recognized to be advantageous in that the treatment of the waste oils can be carried out without heating. There is a problem, however, in safety in such a procedure that, because a gelling agent dissolved in the highly inflammable solvent is used, potential danger of a fire is higher than in the methods (1) to (3). Further, a new waste water which contains solvents and oils is generated and treatment thereof is also burdensome, which results in the treatment being inefficient. Therefore, method (4) is not suitable for the waste-oil-treatment at general homes and food service fields such as restaurants, fast food shops and food supply centers because few possess chemical knowledge.
Method (5) is to solidify water and at the same time trap the oils in the obtained hydrogel body, and is technically different from methods (1) to (4). Method (5) is inefficient in that in such a procedure the amount of disposal to be treated increases because almost the same amount of water as that of oils is necessary, and has a disadvantage in that the solidified product is more difficult to burn than in methods (1) to (4) when incinerated because the solidified product contains a large amount of water.
As described above, each of the methods (1) to (5) has difficulties in efficiency, safety and the like in the waste-oil-treatment and, particularly, cannot be said to be suitable as a method of treating the waste edible oil in general homes.
Further, in general homes, deterioration of qualities such as the hue or viscosity of the edible oil to be used is often noticed just before cooking and it is impossible to take 30 or more minutes for treating (heating and cooling) the waste edible oil as in the methods (1) to (3) by interrupting the cooking. Also, it is assumed that causes that the delay in the spread of the above-mentioned methods lie in technically unsatisfactory aspects such that the hardness of the solidified product changes (is fluid in some cases) every time when waste oils are treated because the amount of the waste edible oil generated from a general home is not always the same and that the hardness of the solidified product cannot be known until 20 or more minutes (until cooled to approximately 40.degree. C.) passes after completion of the heat treatment of the waste oils. From those circumstances, an easy and safe method capable of solidification-treating waste edible oil in a short period of time without heating has been eagerly awaited.
As a method of solidifying waste edible oils and the like without heating, a method (6) is disclosed in JP-A-26246/1995 wherein a composition for treating the waste oils, which contains an oily gelling agent (first component) such as 12-hydroxystearic acid and a low volatile component (second component) which can be heated by electromagnetic energy and facilitates dissolution of the gelling agent into oil, is subjected, alone or after brought into contact with the waste oil beforehand, to heating and melting by providing electromagnetic energy to be dissolved in the waste oil and then allowed to stand. Examples of the second component are bivalent and trivalent polyol, carbitol, butylcarbitol and the like and, particularly preferable are, glycols such as propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, hexylene glycol, octylene glycol and polyethylene glycol, and, further, propylene glycol is most preferable in view of safety of food.
Each of the above-exemplified compounds is, however, included in a category of solvent, for example, as entered in "Shinpan Yozai Pocket Book" (by Yuki Gosei Kagaku Kyokai, published by Oohm Sha Kabushiki Kaisha on June, 1994) and the flashing point thereof, except polyethylene glycol, is in a range of 78.degree. to 140.degree. C. (flashing point of propylene glycol which is the most preferable example is 99.degree. C.). Though each of the compounds has a higher boiling point and lower inflammability as compared with the solvents (dimethyl sulfoxide, N-methylpyrrolidone, ethyl alcohol) used in method (4), the danger of ignition always inherently exits. Therefore, in case where it is assumed that the waste-oil-treatment is carried out in a kitchen where any fire such as gas is always used, even if the composition for the waste-oil-treatment is not directly heated and melted by gas fire, there is a danger that the high temperature composition for the waste-oil-treatment which is heated and melted by another heating means is ignited, which leads to an oil fire. Particularly, the danger of a fire is further increased in such a case where the composition for the waste-oil-treatment is erroneously super-heated.
Though the above-exemplified compounds as the second component are strong in properties as a solvent and, therefore, are superior in capability of dissolving the oily gelling agent (first component) and easy to use, there is a disadvantage that only a solidified product having a relatively low gelling strength can be obtained since a part of the oily gelling agent is still dissolved even after the waste-oil-treatment. In order to produce a solidified product having a high gelling strength, somewhat a large amount of the oily gelling agent (first component) must be used, which leads to an increase cost. With respect to polyethylene glycol, because there is no hydrophobic group in its molecule and the composition for the waste-oil-treatment is not dispersed uniformly in the waste oil, many small lumps of disorderly solidified product are generated in the system and a homogeneously solidified product cannot be obtained.
Also, with respect to a method of preparing the composition for the waste-oil-treatment there is simply described the mixing of components. And, with respect to the method for heating and melting the composition for the waste-oil-treatment, there is described the internal heating by providing electromagnetic energy, though it is not clear whether or not it is for avoiding the above-mentioned problem of ignition. There is described, concretely, a method of heating the gelling agent by means of a microwave oven just before the addition to the waste oils (method 6A), or a method of heating the gelling agent together with the waste oils after the addition (method 6B). Though the heating method 6A by means of the microwave oven is easy to operate, super-heating results in not only the above-mentioned danger of a fire but also unexpected scald, and deterioration of the second component occurs and odor is generated. On the contrary, insufficient heating brings about solidification failure. Therefore, to carry out the waste-oil-treatment safely and surely, it is necessary to change the amount of the composition for the waste-oil-treatment and the heating time of the microwave oven according to the amount and temperature of the waste oils to be treated. It is not possible to expect that housewives of general homes, who have poor chemical knowledge, can be entrusted with such a troublesome task. Also, though it is recognized that the consumption of energy required for the heating in the method 6B is smaller than that in the conventional methods (1) to (3) of heat-treating the waste oils, method 6B is not different from the conventional methods (1) to (3) in such a point that the waste oils are heated. Though there is a description with respect to a heat- and oil-resistive container such as a frying pan which is used for the waste-oil-treatment, there is no description with respect to a container for the composition for the waste-oil-treatment.
The present invention has been completed on the basis of the above-mentioned backgrounds, and the object thereof is to provide a method of solidifying waste oils safely and surely in a short period of time without heating the waste oils and to provide a solidifying agent which can be used with a broad range of compositions.